EARLY UV INGRESS IN WASP-12b: MEASURING PLANETARY MAGNETIC FIELDS
EARLY UV INGRESS IN WASP-12b: MEASURING PLANETARY MAGNETIC FIELDS
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WASP-12b 中的早期紫外线侵入：测量行星磁场
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
Christiane Helling
中科院分区：
文献类型：
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作者：
Aline Vidotto;M. Jardine;Christiane Helling
最近，Fossati et al.观察到，与光学过境相比，WASP-12b的紫外过境表现出更早的进入。我们认为，由此产生的早期进入是由行星轨道运动之前的弓形激波引起的。在这封信中，我们研究了可能导致这种弓形激波形成的条件。我们考虑了两种情况：(1)恒星磁场足够强，可以将炽热的日冕等离子体限制在行星轨道上；(2)恒星磁场无法限制等离子体，等离子体在风中逃逸。在这两种情况下，当等离子体温度为T≲(4-5)×106K时，能够将等离子体压缩到观测密度的激波将在行星周围形成。在受限情况下，激波总是形成在行星的正前方，但在风的情况下，激波的方向取决于风速，因此也取决于等离子体温度。对于较高的风温，激波形成于行星和恒星之间的中心线附近。我们得出结论，激波形成导致可观察到的早期紫外线进入可能是凌日系统的一个共同特征，并可能被证明是设定行星磁场强度BP极限的有用工具。在WASP-12b的情况下，我们推导出约BP=24G的上限。
Recently, Fossati et al. observed that the UV transit of WASP-12b showed an early ingress compared with the optical transit. We suggest that the resulting early ingress is caused by a bow shock ahead of the planetary orbital motion. In this Letter, we investigate the conditions that might lead to the formation of such a bow shock. We consider two scenarios: (1) the stellar magnetic field is strong enough to confine the hot coronal plasma out to the planetary orbit and (2) the stellar magnetic field is unable to confine the plasma, which escapes in a wind. In both cases, a shock capable of compressing plasma to the observed densities will form around the planet for plasma temperatures T ≲ (4–5) × 106 K. In the confined case, the shock always forms directly ahead of the planet, but in the wind case the shock orientation depends on the wind speed and hence on the plasma temperature. For higher wind temperatures, the shock forms closer to the line of centers between the planet and the star. We conclude that shock formation leading to an observable early UV ingress is likely to be a common feature of transiting systems and may prove to be a useful tool in setting limits on planetary magnetic field strengths Bp. In the case of WASP-12b, we derive an upper limit of about Bp = 24 G.
在系外行星 WASP-12b 的轨道上
DOI：
10.1088/0004-637x/727/2/125
发表时间：
2011
期刊：
The Astrophysical Journal
影响因子：
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作者：
Campo C
通讯作者：
Campo C